This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The TrkH/TrkG/KtrB proteins mediate K+ uptake in bacteria and likely evolved from simple K+ channels by multiple gene duplications or fusions. In contrast to tetramerization architecture of usual potassium channels, all four subunits of TrkH are expressed in a single peptide. Atomic structure of TrkH protein will reveal the new features of its assembly and help people understand the mechanism of ion permeation and gating.